Acceleration sensors have been used for detecting shock externally applied to electronic devices such as hard drives. A known example of an acceleration sensor, such as the one disclosed in Japanese Unexamined Patent Application Publication No. 2005-315847, has a single-end support structure in which one longitudinal end of a piezoelectric vibrating element, which includes strip-shaped piezoelectric substrates bonded to each other and charge detecting electrodes disposed on opposite principal surfaces thereof, is supported by a support member.
In an acceleration sensor equipped with a piezoelectric vibrating element, the piezoelectric vibrating element bends in response to applied acceleration and causes the piezoelectric substrates to warp. An electric charge produced by a piezoelectric effect is extracted by the charge detecting electrodes on the opposite principal surfaces so that the acceleration is detected. Therefore, in an acceleration sensor with a single-end support structure in which one longitudinal end of the piezoelectric vibrating element is supported, the piezoelectric vibrating element bends by a greater amount in response to applied acceleration, as compared with an acceleration sensor with a double-end support structure in which the opposite longitudinal ends of the piezoelectric vibrating element are supported. Consequently, an acceleration sensor with a single-end support structure can achieve higher acceleration-detecting sensitivity.
However, the acceleration sensor proposed in Japanese Unexamined Patent Application Publication No. 2005-315847 has several problems due to having a structure in which a stationary frame having a through-hole is set in an opening in one surface of a box-shaped casing and the piezoelectric vibrating element is securely fitted and positioned in this through-hole.
The first problem is that size reduction is difficult. With the structure in which the piezoelectric vibrating element is fitted in the through-hole of the stationary frame disposed in the opening in one surface of the box-shaped casing, the distance between an end of the piezoelectric vibrating element fitted in the through-hole and an inner wall surface of the casing cannot be accurately ascertained during assembly. For this reason, the distance between the end of the piezoelectric vibrating element and the inner wall surface of the casing cannot be reduced, making it difficult to achieve size reduction.
The second problem is in the difficulty in manufacture due to a complex structure. Since this complex structure is assembled using many components having complex shapes, such as the box-shaped casing having the opening in one surface thereof and the stationary frame having the through-hole in which the casing is set, the manufacturing process is difficult.